Compact drive unit including juxtaposed tracks

ABSTRACT

The drive unit includes a watertight elongated housing extending along a longitudinal axis and defining an inner chamber, two juxtaposed tracks disposed around the housing along its longitudinal axis and enabling the drive unit to move when the tracks are rotatably driven around the housing, and at least one track-driving motor. The motor is located within the inner chamber of the housing and includes an output shaft mechanically connected to the corresponding track. The unit can also include a ventilation circuit for the interior of the inner chamber of the housing, and a generator for producing electricity. The drive unit can be manufactured from a single housing or with the housings of two apparatuses that are juxtaposed and rigidly paired.

CROSS REFERENCE TO PRIOR APPLICATIONS

The present case is a continuation of PCT patent application No.PCT/CA2012/050747 filed on 19 Oct. 2012. The present case is also animprovement of the concept disclosed in patent application No.PCT/CA2011/050202 filed on 15 Apr. 2011 by the same inventor.PCT/CA2011/050202 and PCT/CA2012/050747 are both integrally incorporatedby reference to the present case.

TECHNICAL FIELD

The technical field relates generally to compact pulling apparatuses andto compact drive units capable of travelling over difficult terrains,such as terrains covered with snow, sand, mud, etc.

TECHNICAL BACKGROUND

Various apparatuses have been suggested over the years for travelling ondifficult terrains. Of these, several are compact apparatuses allowingone person, such as a person on skis, to be pushed or pulled using atrack rotatably driven by a motor. Examples can be found in documentsFR-2,431,304 (Jaulmes) published on 15 Feb. 1980 and in U.S. Pat. No.4,519,470 (Allisio) published on 28 May 1985. Numerous other examplesexist. Most of these apparatuses use a gasoline engine to rotatablydrive the track. Some use an electric motor. Apparatuses of this sortcan be useful as light means of transportation, especially where it isdifficult or even forbidden to travel using a larger vehicle. Forexample, in terrains with a snow-covered surface, the snow could be toopowdery or too deep to use a snowmobile. Another advantage of suchapparatuses is that it is much simpler and easier to transport them inanother vehicle than is the case with a larger and heavier vehicle, forinstance a snowmobile.

Unfortunately, none of these previously-suggested apparatuses has provenfully adapted to the very rigorous winter conditions encountered duringparts of the year in places where such apparatuses are likely to beuseful. For instance, a very cold temperature can significantly hinderthe reliability and the autonomy of an apparatus having an electricmotor powered using batteries. In the case of a gasoline engine, thecombination of cold weather and heat released from the engine can causeice and compacted snow to build up at sensitive points of the apparatus.Moreover, milder temperatures are more likely to cause waterinfiltrations into the apparatus, which can then result in failuresdifficult to repair, especially if they occur deep into the forest or inother places that are difficult to access.

Also, the previously-suggested apparatuses do not allow an electricgenerator and/or a payload to be easily transported to places that aredifficult to access, for instance places where space is limited, onrough terrains and/or on very soft terrains.

PCT patent application No. PCT/CA2011/050202, published on 20 Oct. 2011under number WO 2011/127607, presents significant improvements in therelated technical field. This patent application is from the sameinventor as the present application. WO 2011/127607 discloses, amongother things, various embodiments of a compact pulling apparatus thatcan easily travel on difficult terrains, such as terrains covered withsnow, sand, mud, etc. This apparatus opens the way to many otherimprovements in the transport sector in general. Several solutions toproblems and to specific needs in this general area have been suggested,such as having an improved drive unit can be used in manyimplementations.

SUMMARY

According to one aspect, there is provided a transport drive unit,including: two compact pulling apparatuses that are juxtaposed andrigidly paired, each apparatus including: a watertight elongated housingextending along a longitudinal axis and defining an inner chamber, thehousing including a top wall and a bottom wall; a track disposed aroundthe housing along its longitudinal axis; a track-driving motor, themotor being located within the inner chamber of the housing andincluding an output shaft mechanically connected to the track; and aventilation circuit for the inner chamber of the housing, theventilation circuit including an air inlet and an air outlet whichcommunicate with outside of the housing, the ventilation circuitallowing the temperature within the inner chamber to be kept above thefreezing point when the outside temperature is lower and allowing theinterior of the inner chamber to be cooled when its temperature exceedsan upper threshold.

According to another aspect, there is provided a transport drive unitincluding: a watertight elongated housing extending along a longitudinalaxis and defining an inner chamber, the housing including a top wall anda bottom wall; two juxtaposed tracks disposed in parallel around thehousing along its longitudinal axis and which enable the unit to movewhen the tracks are rotatably driven around the housing; at least onetrack-driving motor, the motor being located within the inner chamber ofthe housing and including an output shaft mechanically connected to atleast one of the tracks; and a ventilation circuit for the inner chamberof the housing, the ventilation circuit including an air inlet and anair outlet which communicate with outside of the housing, theventilation circuit allowing the temperature within the inner chamber tobe kept above the freezing point when the outside temperature is lowerand allowing the interior of the inner chamber to be cooled when itstemperature exceeds an upper threshold.

According to another aspect, there is provided a method of using atransport drive unit of the type including a watertight elongatedhousing extending along a longitudinal axis and defining an innerchamber inside which a motor is located, and also including twojuxtaposed tracks disposed around the housing along its longitudinalaxis and which enable the apparatus to move when at least one of thetracks is rotatably driven around the housing by the motor; the methodincluding the following simultaneous steps: maintaining a minimumtemperature in the inner chamber using heat released from the motor ormotors; evacuating heat from within the inner chamber if the temperatureexceeds a given threshold; maintaining a positive pressure within theinner chamber in operation; simultaneously using the two tracks to movethe drive unit; and moving at least a payload that is temporarily placedon the drive unit.

According to another aspect, there is also provided a method formanufacturing a unit as previously defined.

According to another aspect, there is also provided the use of a driveunit as previously defined, wherein the unit travels over a snow-coveredterrain and/or a rough terrain and/or a muddy terrain.

More details on these aspects, as well as on other aspects of theproposed concept, will become apparent in light of the detaileddescription which follows and the appended figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is an isometric view of an example of an apparatus illustrated inPCT patent application No. PCT/CA2011/050202 published under number WO2011/127607, this example using an internal-combustion engine;

FIG. 2 is a side view of the apparatus shown in FIG. 1;

FIG. 3 is a view similar to FIG. 1 but shows the apparatus without itstrack and without the lateral walls on the sides of its housing;

FIG. 4 is a view similar to FIG. 3 but shows the left side of theapparatus, as seen from the rear;

FIG. 5 is a right side view of the apparatus shown in FIG. 3;

FIG. 6 is a view similar to FIG. 1 but where the operator is standing ona sled hitched to the apparatus;

FIG. 7 is a view similar to FIG. 3 but shows a second example of anapparatus based on the proposed concept in WO 2011/127607, this exampleusing an electric motor;

FIG. 8 is a view similar to FIG. 7 but shows the left side of theapparatus, as seen from the rear;

FIG. 9 is a right side view of the apparatus shown in FIG. 7;

FIG. 10 is a semi-schematic front view showing an example of a compactdrive unit in accordance with the proposed concept;

FIG. 11 is a semi-schematic side view showing another example of acompact drive unit in accordance with the proposed concept, this unitincluding a dump body;

FIG. 12 is a view similar to FIG. 11 in which the dump body is shown ina tilted position;

FIGS. 13 to 21 are top schematic views illustrating different examplesof configurations inside the compact drive unit;

FIG. 22 is a block diagram that schematically shows an example of acontrol for the drive unit;

FIG. 23 is a top view of an example of a drive unit in accordance withthe proposed concept; and

FIG. 24 is a view similar to FIG. 23 and illustrates another example ofdrive unit in accordance with the proposed concept.

DETAILED DESCRIPTION

FIG. 1 is an isometric view of an example of an apparatus 10 illustratedin PCT patent application No. PCT/CA2011/050202 published under numberWO 2011/127607. FIGS. 2 to 9 are also views from this same PCTapplication. FIGS. 1 to 9 as well as the following description textabout these figures are provided for reference purposes. The proposedconcept in the present application includes improvements over what isshown in FIGS. 1 to 9 and offers new possibilities.

In the example of FIG. 1, the apparatus 10 uses an internal-combustionengine to rotate a track 12 disposed around a watertight housing 14having an elongated shape. It should be noted at this point that thereference to a “watertight” housing means that its construction iswatertight but this does not exclude the presence of a ventilationcircuit for the interior of the housing 14. This ventilation circuitincludes at least one air inlet and at least one air outlet. Theventilation circuit makes it possible, among other things, to cool theinterior of the housing 14 when its temperature exceeds an upperthreshold, for example above 25° C. Other values are also possible.

The rotation of the track 12 around the housing 14 enables the apparatus10 to move. The housing 14 is low-slung in order to keep its center ofgravity as low as possible. The housing 14 includes a lateral wall 16 oneach side, which can be made removable to facilitate access to theinterior. The housing 14 can, for instance, be made of a metallicmaterial, of a plastic material, or both. Aluminum is an example of onepossible material for the housing 14 since this material is light andstrong. The track 12 can be made of rubber or of another polymer. Othermaterials are possible.

The apparatus 10 of this example includes a handlebar 20 which isconnected to the housing 14. The handlebar 20 extends substantiallyrearward of the apparatus 10. The handlebar 20 is intended to be heldand manipulated by an operator 22 who is at the rear of the apparatus10, as shown in a semi-schematic manner in FIG. 1. The handlebar 20 canbe pivotal or fixed, depending on the needs. When pivotal, it ispossible to limit the pivoting of the handlebar 20 between a minimumangle and a maximum angle with reference to the horizontal. Thehandlebar 20 could also be omitted in certain embodiments or even bereplaced by another arrangement.

The operator 22 can be provided with skis 24 (or the equivalent) or beon board a sled hitched to the apparatus 10 (FIG. 6). As can be seen inFIG. 1, the center of gravity of the apparatus 10 is at a height that isbelow the knees of the operator 22.

The operator 22 of the apparatus 10 shown in FIG. 1 has controls (notshown) available on the handles of the handlebar 20 which allow, amongother things, controlling the travel speed of the apparatus 10 and otherfunctions. The controls can be connected to the housing 14 using wiresand/or by wireless communication means. Depending on the model, it is,among other things, possible to provide an arrangement which enables theapparatus 10 to back up by its own motor power, which can be very usefulin certain circumstances. Levers for operating a brake can also beprovided. These levers can be placed similarly to those of the brakes ona bicycle or a motorcycle, for instance. Other elements can be providedon the handlebar 20 according to the needs, such as a lamp, indicatordials, etc. Many other variants are possible.

When travelling forward, the apparatus 10 pulls the operator 22 alongand, if applicable, moves a payload, for instance a payload placed onboard a sled hitched to the apparatus 10. Such apparatus 10 can easilypull a load equivalent to twice its own weight in powder snow. Forexample, tests carried out using an apparatus weighing 125 kg (275 lbs)have shown that such an apparatus, even alone, was able to pull a loadof 225 kg (550 lbs) over a distance of 150 km on a single fuel tank.

The operator 22 of the apparatus 10 shown in FIG. 1 can change thetravel direction of the apparatus 10 by moving the handlebar 20 sidewaysin the direction opposite the turn to be made. This action is similar tothe one made by the operator of a small conventional lawn mower.Variants are also possible.

FIG. 2 is a side view of the apparatus 10 shown in FIG. 1. FIGS. 1 and 2show the assembled apparatus 10. FIG. 3 is a view similar to FIG. 1 butshows the apparatus without its track 12 and without the lateral walls16 on the sides of its housing 14. FIG. 4 is a view similar to FIG. 3but shows the left side of the apparatus 10, as seen from the rear. FIG.5 is a right side view of the apparatus 10 shown in FIG. 3.

As can be seen, especially in FIGS. 3 and 4, the housing 14 defines aninner chamber 30 in which different components of the apparatus 10 arelocated, such as its internal-combustion engine 32. The housing 14 alsoincludes a top wall 14 a, a bottom wall 14 b, a front wall 14 c and arear wall 14 d. The housing 14 has a reinforced structure which caninclude one or several internal walls to divide the inner chamber 30.The compartments communicate with each other.

A pair of top skids 34 is disposed longitudinally on the top wall 14 aof the housing 14. A pair of bottom skids, similar to those on the topwall 14 a, is disposed longitudinally on the bottom wall 14 b of thehousing 14. The skids are made of a material having a very low frictioncoefficient. They allow, among other things, the track 12 to rotatearound the housing 14 and to reduce friction between the inner face ofthe track 12 and the exterior of the housing 14. They also serve asguides to keep the track 12 in registry with the axis of the apparatus10. The skids extend for several centimeters beyond the front and rearends of the top wall 14 a and of the bottom wall 14 b so as to supportthe track 12 along almost the entire length of the apparatus 10.Variants are possible.

At least one front roller is rotatably connected on the front of thehousing 14. In the illustrated example, two front rollers 40 areprovided. The front rollers 40 are coaxially mounted around a fronttransversal axle 42 which is supported by an internally-greased axleconnected at its ends to two opposite plates 44 which are disposedparallel to the longitudinal axis of the apparatus 10. The plates 44 arerigidly connected to the front of the housing 14. Also in theillustrated example, a bumper 46 is provided at the front of theapparatus 10. The ends of the bumper 46 are connected to the two plates44, as shown for instance in FIGS. 3 and 4. Sufficient clearance isprovided between the interior of the bumper 46 and the front rollers 40to allow the track to rotate around the housing 14 without interferingwith the interior of the bumper 46. Variants are also possible.

At least one rear roller is rotatably connected at the rear of thehousing 14. In the illustrated example, two rear rollers 50 areprovided. The rear rollers 50 are coaxially mounted around a reartransversal axle 52, which is supported at its ends by bearings locatedin two opposite plates 54 disposed parallel to the longitudinal axis ofthe apparatus 10. The plates 54 are rigidly connected to the rear of thehousing 14. Also in the illustrated example, a mechanical connection isprovided between the output shaft of a transmission 60 located withinthe housing 14 and the rear transversal axle 52. The rear rollers 50 arethus used to drive the track 12 in rotation so as to move the apparatus10. Different types of mechanical connections can be used between thetransmission 60 and the rear transversal axle 52. The illustrated oneincludes a drive belt 62 or a chain and provides a reduction of therotation speed between the output shaft of the transmission 60 and therear transversal axle 52. Other types of connections and configurationsare also possible. The mechanical connection between the engine 32 andthe transmission 60 is provided by a drive belt 64. The transmission 60can enable either a forward or reverse motion, for instance. It can haveone or more speeds or be a variable speed transmission. Numerous othervariants are possible.

The rear transversal axle 52 also carries a brake disk 66, which isshown in FIG. 4. The disk is disposed near the left end in the example.The brake pads are attached to the housing 14 and can be operated by theoperator 22 from the handlebar 20.

The engine 32 for the track 12 of the example illustrated in FIGS. 1 to4 is an internal-combustion engine and is located immediately in frontof the transmission 60. An intermediary transversal wall is present inthe illustrated example so as to reinforce the area between theinternal-combustion engine 32 and the transmission 60. Theinternal-combustion engine 32 is supplied with fuel from a tank 70located at the front of the inner chamber 30 of the apparatus 10. Abattery 72 is disposed beside the fuel tank. This battery 72 is, amongother things, provided to power the electric starter of theinternal-combustion engine 32. The operator 22 is thus able to start orto stop the engine 32 without having to access it directly. Variants arealso possible.

The apparatus 10 shown in FIGS. 1 to 5 also includes a generator 80provided in the inner chamber 30 and that can produce electricityintended to power one or more external equipment at a voltagecorresponding for instance to that of a domestic electrical outlet, forexample 110 V or 220 V/240 V at 60 Hz or also at 50 Hz. One or moreelectrical sockets are available on the apparatus 10 or on the generator80 itself. The generator 80 includes an internal rotor which can berotatably driven by the same internal-combustion engine 32. Thepossibility of generating electricity within the apparatus 10 can bevery advantageous to users such as workers operating power tools atremote sites, or to owners of cottages located far from inhabited areas.Many other uses can be devised. A generator with a power rating of 4000to 6000 W can be provided within an apparatus 10 of the size shown inFIGS. 1 to 5. Using a smaller or even a larger generator is alsopossible.

The axis of the generator 80 is disposed transversely with reference tothe longitudinal axis of the apparatus 10 in the example. The generator80 could also be disposed in some other way in certain models, forinstance using an angular gearbox. It is connected to the output shaftof the internal-combustion engine 32 by a drivebelt 82. An electricclutch 84, provided on the shaft of the generator 80, allows themechanical connection between the generator 80 and theinternal-combustion engine 32 to be engaged or disengaged remotely.Thus, when there is no need for the generator 80 to be used, forinstance when the apparatus 10 is in motion, unnecessary rotation of therotor of the generator 80 can be avoided. When the generator 80 is inoperation, the transmission 60 of the apparatus 10 is set to neutral.Variants are also possible.

The admission of fresh air into the interior of the inner chamber 30 ofthe housing 14 is effected through a series of apertures 90 provided onat least one lateral side of the housing 14, immediately beneath the topwall 14 a. These apertures 90 have a relatively small diameter so as tominimize snow and debris ingestion, such as twigs or others. Air passingthrough the apertures 90 goes into an inlet box 92 which collects theair coming from all the apertures 90 on each side of the housing 14.When the apparatus 10 is in use, the inlet box 92 is heated from belowby the heat released from the internal-combustion engine 32 and whichcirculates in the inner chamber 30. This heat allows the inner chamber30 to be kept well above freezing point (0° C.) even if the outsidetemperature is very cold, for example below −20° C. With this heat, anysnow particle entering the inlet box 92 can melt and drip out toward theexterior, even during cold weather. The air exits the inlet box 92through an exit pipe 94 which is circular in the example. The top of theexit pipe 94 can be raised several millimeters above the bottom of theinlet box 92 so as to prevent the flow of water directly toward theinner chamber 30.

The apparatus 10 includes an air inlet box. Air leaving the inlet box isthen channeled into a flexible duct 95 (schematically illustrated inFIG. 4) leading to the inlet 33 of the cooling fan shroud located on theinternal-combustion engine 32. The fan in the engine 32 thus generatesthe necessary suction force to draw air through the apertures 90. Thecooling air passes around the cylinder or cylinders of theinternal-combustion engine 32 and ends up in the interior of the innerchamber 30.

Variants of what is described in the preceding paragraphs are possible.

The evacuation of air from the interior of the apparatus 10 is effectedin two ways. On the one hand, the combustion of fuel in the engine 32generates exhaust gases. The air used in this combustion process isadmitted into the interior of the engine 32 from the interior of theinner chamber 30 or it can also come directly from the inlet box 92 forsome engines. The exhaust gases coming out of the cylinder or cylindersof the engine 32 are then directed toward the rear of the apparatus 10using an exhaust pipe. The exit of the exhaust pipe is located in aspace where the rear transversal axle 52 and the two rear rollers 50 arelocated. This space is partially blocked by the presence of the track 12when the apparatus 10 is assembled. This configuration, among otherthings, reduces noise as well as prevents any possible contact betweenthe skin or cloths of the operator 22 and the hot exit of the exhaustpipe. Other configurations are also possible.

Some air is also evacuated from the interior of the inner chamber 30through an air outlet which forms part of the ventilation circuit. Airpassing through the outlet goes first into the cooling circuit of thegenerator 80 and then flows through a flexible duct 104 (shownschematically in FIG. 4) up to the inlet of an air outlet box 100. Theoutlet box 100 has a similar structure to that of the inlet box 92. Theair is then evacuated through the apertures 102 located on at least onelateral side of the housing 14. Variants are also possible.

When the generator 80 is in operation, the fan integrated into thegenerator 80 contributes to the displacement of air so as to increasethe air flow that cools it. Additional fans disposed in series on theflexible ducts connected to the air inlet and to the air outlet canfurther increase the air flow if the temperature inside the innerchamber 30 becomes too high. These fans can be automatically switched onusing a thermostat provided with a temperature sensor or anotherarrangement.

The apparatus 10 is configured in such a way that a positive pressure iscreated in the inner chamber 30. This is achieved by providing anoverall air inlet area greater than the overall air outlet area. In theexample, the number of apertures 90 is greater than the number ofapertures 102. The positive pressure, among other things, improves thewatertightness of the housing 14.

When the apparatus 10 is in motion, the sides of the housing 14 areclosed in a watertight manner using the lateral walls 16 that are shownin FIGS. 1 and 2. These lateral walls 16 are bolted or are otherwiseattached to the rest of the housing 14. The interior of the housing 14thus remains watertight and dry while the apparatus 10 is in use.

As is shown in FIG. 5, the underside of the housing 14 is convex at itscenter. This heightening is about 3 cm at the front and at the rear ofthe track 12 in the apparatus 10 of the illustrated example. Thiscentral part corresponds to about one third of the length of theapparatus 10. The heightening, among other things, facilitates a yawingmotion when making a turn as well as the manual pivoting of theapparatus 10 on hard and rough surfaces, for example on asphalt orconcrete. Moreover, the front of the bottom wall 14 b defines an anglewith reference to the horizontal. The front transversal axle 42 is thushigher than the rear transversal axle 52. This also facilitates passageover obstacles. Variants are also possible.

FIG. 6 is a view similar to FIG. 1 but where the operator 22 is standingon a sled 200 hitched to the apparatus 10. The hitch 202 of the sled 200is connected to a support 210 which, in the illustrated example, is inthe form of a transversal strut that is straight or slightly curvedtowards the rear at its center. The transversal strut 210 is supportedusing two corresponding plates 212 projecting towards the top of thehousing 14. The hitch 202 includes two retainer arms of the sled 200,which arms are attached to a plate 204 that can pivot around a verticalaxis where it joins a fastening element 206. The fastening element 206can slide left and right along the transversal strut 210 using twopulleys provided on either side of the fastening element 206. In a turn,the fastening member 206 can thus move toward one of the ends of thetransversal strut 210, this facilitating handling of the apparatus 10and reducing the effort required from the operator 22. Variants are alsopossible. FIGS. 7 to 9 show a second example of an apparatus 300 inwhich an electric motor is used. This apparatus 300 is otherwise similarto the apparatus 10 shown in the previous example. The apparatus 300includes, among other things, a track 302, a watertight housing 304 anda handlebar 306, which handlebar is held by an operator 308. Theapparatus 300 can also be used with the sled 200 in FIG. 6.

The track 302 of the apparatus 300 is rotatably driven by an electricmotor 310. This motor 310 is powered using electricity from one orseveral batteries 312, which are also located within the inner chamber314 of the housing 304. The electric motor 310 can either be of type ACor DC, with or without permanent magnets. A group of four deep cyclelead batteries 312 is shown in the illustrated example. The number andthe type of batteries 312 can differ according to requirements. Thebatteries 312 are connected to an electric controller which the operator308 controls from the handles of the handlebar 306. The variouselectrical connections are not shown in the figures so as to simplifythe illustrations.

In use, the electric motor 310 releases heat. This heat often accountsfor about 10% of the electrical energy drawn from the batteries 312. Theheat thus dissipated is used within the inner chamber 314 of theapparatus 300 to keep the batteries 312 warm when the outsidetemperature is very cold. This heat thus makes it possible to keep thebatteries at an optimal temperature despite very cold weather. Theoptimal temperature can be for instance in the range of 20 to 25° C.Other temperatures are also possible. This heat recovery is beneficialbecause most batteries lose their efficiency in cold weather. This isparticularly the case of lead batteries. Although other batteries withbetter performance exist, lead batteries remain an attractive choicebecause they are easily available and relatively inexpensive. Theywithstand cold weather better than nickel or lithium batteries forinstance. However, the efficiency of lead batteries diminishes almostlinearly with reference to temperature, going for example from 100% at25° C. down to 30% at −40° C., depending on the exact type of battery.The decrease in efficiency thus has a direct impact on the autonomy ofthe apparatus 300. By keeping the heat inside the housing 304 duringcold weather, the batteries 312 can then maintain a much higherefficiency than that at low temperatures. The interior of the housing304 can also be insulated to help conserve heat. Variants are alsopossible.

An internal ventilation circuit is provided in case of overheating, forexample when the apparatus 300 is operating in relatively mild weatherand the electric motor 310 is intensively solicited. This internalventilation circuit is part of the ventilation circuit. It can include athermostat which activates at least one fan providing a supply of airfrom the outside to dissipate interior heat. The air inlet and the airoutlet can be located in the top part of the handlebar 306 at a certaindistance from one another. The air then circulates in the tubes formingthe sides of the handlebar 306. The fan or fans can be provided in thehousing 304 or alternatively in the handlebar 306. The junction betweenthe handlebar 306 and the housing 304 is configured so as to provide anair passage between them. This way, the housing 304 can have a verywatertight structure up to the height of the air inlet and the airoutlet on the handlebar 306. A positive pressure is maintained withinthe interior of the inner chamber 314 to mitigate the risks of havingwater infiltration at locations which may not be completely watertight.The apparatus 300 can then even be immersed in water from time or time,as might be required for instance when the apparatus 300 must cross anunfrozen stream or a similar body of water.

It is possible to provide a heating element, for instance a heatingcable, inside the housing 304 to keep the batteries 312 warm when theyare being charged outdoors during cold weather and also while they arebeing stored outdoors.

FIG. 10 is a semi-schematic front view showing an example of a compactdrive unit 400 in accordance with the proposed concept. The drive unit400 includes two compact pulling apparatuses 10 as a base and also toprovide the motorized arrangement. The two apparatuses 10 of the driveunit 400 are juxtaposed and rigidly paired. The housings of theseapparatuses 10 are thus part of the frame of the drive unit 400.

In FIG. 10, each of the apparatuses 10 includes an internal-combustionengine therein. Their configuration could be, for instance, similar tothat shown in the example of FIGS. 3 to 5. Numerous variants are howeverpossible. It could even be possible to use more than two juxtaposedapparatuses 10. It must be understood that the reference to the presenceof two apparatuses 10 can include the case where there are more than twoapparatuses 10.

In the example illustrated in FIG. 10, each apparatus 10 includes, amongother things, a watertight housing, a track 12 disposed around thehousing along its longitudinal axis, a driving motor for the track 12and a ventilation circuit for the inner chamber of the housing. The twotracks 12 are then in juxtaposition and at a close distance from oneanother. Yet, this configuration allows positioning the tracks 12 at adistance of 3 inches (76 mm) or less between their corresponding inneredges. It is still possible to position the tracks 12 at a greaterdistance. However, it was found that a distance of 3 inches (76 mm) orless is very advantageous to reduce the likelihood or even completelyavoid introducing debris, such as rocks or others, into the interveningspace. Such debris could otherwise block the drive unit 400 and requirean intervention from the operator. The tracks 12 can be positioned at avery small distance from one another, this distance being even possiblyless than 1 mm in some embodiments so as to optimize the ground bearingand reduce the likelihood of getting bogged down on soft grounds. Theminimum distance to be maintained will often depend on the amplitude ofthe lateral displacement of the tracks 12 in use. Even in normal use,the tracks 12 may move slightly off their longitudinal axis, especiallyfor example in tight turns. Other similar situations also exist.

FIG. 10 also illustrates the fact that the drive unit 400 can beconfigured for receiving a transport rack 402 or any similar structureof the same nature that can be positioned above the tracks 12. Thistransport rack 402 can be useful for carrying equipment or materials, toname just these two examples. The drive unit 400 then acts as a payloadtransport vehicle. The loading capacity of the drive unit 400 issignificantly increased by the fact that two apparatuses 10 are paired.The operator can control the drive unit 400 in various ways, for examplewith the handlebar 20. The handlebar 20 may be shifted laterally tocreate a moment of force urging the drive unit 400 to turn.

Some embodiments may include controls at the level of the handlebar 20.It could also be possible to place the controls elsewhere than on thehandlebar 20. The steering controls can be provided to steer the driveunit 400 using mechanical force coming from the drive unit itself. Forexample, the rotation speed of one of the tracks 12 around its housingcould be different from the rotation speed of the other track 12. It mayeven be possible to stop the rotation of one of the tracks 12 while theother track 12 is in motion. Another possibility is to reverse thedirection of rotation between the two tracks 12. This asymmetry in themotion of the tracks 12 will then create a moment of force to change thedirection of the drive unit 400.

To achieve control of the rotation of the tracks 12 independently fromone another, it is possible to use a motor for each of the tracks 12. Afurther possibility is the use of a differential which, when providedtogether with an independent braking system on each side of the driveunit 400, including a disk or others, can create a rotation speeddifference between the two tracks 12. For example, in this case, it canbe possible to brake the track 12 on the left so as to increase thepower transferred to the track 12 on the right and thereby cause thedrive unit 400 to pivot to the left. To turn right, one only needs toexecute the opposite action, thus braking the right side. Otherpossibilities also exist. For example, using an electrical or electroniccontrol is possible. One example of electrical control is a pair ofpotentiometers, each placed on one of the handles of the handlebar 20 inorder to measure the position of corresponding levers actuated by theoperator. An example of an electronic control is a lever similar to a“joy stick”, which allows a control without physical effort and with ahigh accuracy. One can find such arrangement on motorized wheelchairs.The use of a control in the form of a steering wheel or a pivotinghandlebar, like as the one on a motorcycle for instance, is possible.Many more variants can be considered.

FIG. 11 is a semi-schematic side view showing another example of a driveunit 400 according to the proposed concept. This figure illustrates adrive unit 400 provided with a dump body 410 placed above. This dumpbody 410 has a width that is equivalent to the width of the drive unit400. Other configurations are also possible. Adding a dump body 410 tothe drive unit 400 then transforms it into the dumper. Such dumper canbe used to transport bulk materials, for instance earth, sand, gravel,wood, or any other materials or cargo, to places that are otherwisedifficult to access using any other kind of vehicle. The low height ofthe dump body 410 from the ground keeps the center of gravity extremelylow, which substantially increases the stability of the drive unit 400on a rugged terrain and particularly in slopes. The height of the centerof gravity is also very low since the entire motorized arrangement andthe heavier components are in the housing, thus very close to theground. The low height of the dump body also reduces the effort requiredfor loading materials, which is a very important advantage to facilitatethe work to be done during loading. This advantage is also present whenusing a fixed transport rack 402 (FIG. 10) instead of one with a dumpbody 410.

FIG. 11 also schematically illustrates a platform 420 on which theoperator can stand when the drive unit 400 travels, thus preventing theoperator from having to walk behind the drive unit 400. The exactlocation and the precise shape of the platform 420 are conceived so thatthe operator can easily get on and get off it. The platform 420 may beomitted in some configurations but remains interesting since the driveunit 400 will often be used on difficult terrains, for instance onsnow-covered terrains and/or on rough terrains and/or on muddy terrains,thus where waling could be difficult. An example of a rough terrain isone with a large number of rocks, tree trunks, holes in the ground, etc.Other situations also exist. In the context of the present case, aterrain covered with a relatively thick layer of sand is the equivalentof a snow-covered terrain if the sand is dry, or is the equivalent of amuddy terrain if the sand is damp, wet or covered with water.

Alternatively, the drive unit 400 could be used by an operator wearingskis, as shown in FIG. 1, or by an operator standing in a sled, as shownin FIG. 6. It should be noted that depending on where the drive unit 400will be used, the sled can include one or more wheels, thus be atrailer. The sled could also be fitted with skis. Many other variantsare possible.

FIG. 12 is a view similar to FIG. 11 in which the dump body 410 isillustrated in a tilted position. This tilting can be motorized or not.For example, in the case of a motorized tilting, the drive unit 400 caninclude a hydraulic system, a pneumatic system or another system thatcan be selectively operated by the operator to change the angle of thedump body 410 and thus be able to easily lay the materials at thedesired location. This system, built-in on the drive unit 400, isschematically depicted by element 430. Some configurations, however, maynot require a motorized tilting arrangement and may require instead anentirely-manual action by the operator. In such a case, one or moresprings could be used to compensate the weight of the dump body. Othervariants are also possible.

It should be noted that in FIG. 12, the pivots and the other fastenersfor the dump body 410 are not shown.

FIGS. 13 to 21 are top schematic views illustrating different examplesof configurations of the compact drive unit.

In FIG. 13, the two juxtaposed apparatuses are directly coupled to oneanother. As aforesaid, the two juxtaposed apparatuses 10 in FIG. 10 arerigidly paired, namely that they are completely made integral with oneanother. There is thus, for instance, no pivoting between them. They canbe bolted directly to one another, for instance using bolts 432 or otherfasteners, or be otherwise interconnected using one or more connectionelements.

In FIG. 14, the two apparatuses 10 are slightly spaced apart and areattached using connectors 432. FIGS. 13 and 14 also show the relativeposition of the tracks 12.

FIG. 15 shows another possible embodiment. It is a drive unit 400 inwhich the motor arrangement is located inside a single housing 450.However, the drive unit 400 still has the configuration in which the twotracks 12 are juxtaposed and thus parallel to one another. The advantageof having a single housing 450 is the larger space it provides. Theconfiguration with two juxtaposed apparatuses 10 is still veryinteresting since it allows, when apparatuses 10 are already built in asingle-track version, using at least some existing parts. The additionalwalls and partitions of a version with two juxtaposed and pairedapparatuses 10 will also provide a greater strength and rigidity to thedrive unit 400.

In the case of two juxtaposed apparatuses 10, the two apparatuses 10 canbe similar or be of different nature, depending on the needs. Forinstance, FIG. 16 schematic shows two apparatuses 10, each having anelectric motor 310 and a plurality of batteries 312. The batteries 312provide power to the corresponding motor 310. It is however possible toprovide interconnections between the batteries 312 on each side.

FIG. 17 schematically shows two apparatuses 10 provided withinternal-combustion engines 32. Each internal-combustion engine 32 isconnected to a corresponding transmission 60. Still, in this example,each internal-combustion engine 32 can also drive a correspondinggenerator 80. This configuration creates a dumper said to be a“generator” when the drive unit 400 is provided with a dump body as inFIGS. 11 and 12. The generator 80 could be omitted in one or the twoapparatuses 10, depending on the needs.

A configuration as shown in FIG. 17 can require changing the internallayout of some elements in one of the two apparatuses 10 when the designof these models was made for a single track. The elements are then movedfor taking into account the fact that the apparatus 10 is located on theleft or on the right in the drive unit 400, whichever is applicable.Also, the apertures for the air inlet are preferably on the exteriorlateral side. However, the air outlet and also the exhaust of theinternal-combustion engines 32 could be shared between the twoapparatuses 10, if required. It is possible for instance to provide ashared outlet in the intervening space, thus in-between the housings ofthe two apparatuses 10. It is also possible to provide an exhaust outleton the respective lateral side, or even on a single one of the twolateral sides.

In FIG. 18, one of the apparatuses 10 is provided with aninternal-combustion engine 32 with a generator 80, and the otherapparatus 10 includes an electric motor 310 and batteries 312.

Whether in one or the other of the possible configurations forjuxtaposed apparatuses 10, for example those shown in FIGS. 16 to 18,some of the spaces or even all of the spaces within the housings can beinterconnected through apertures and/or ducts, so that the pressure bethe same between them when a positive pressure is maintained duringoperation. The ventilation circuit of each apparatus 10 can therefore beshared, each then forming a part of the ventilation circuit of theoverall drive unit 400.

In FIG. 19, the drive unit 400 includes a single internal-combustionengine 32, which is connected to a transmission 60 and also, in thisexample, to a generator 80. The transmission 60 conveys the drivingpower to each track 12. It can also include a differential so that therotation speed of the tracks 12 be different. Nevertheless, in someimplementations, in particular when the transported weights arerelatively small, one can simply use a transmission without adifferential. The rotation speed to the tracks 12 would then always bethe same. In this case, the operator can steer the drive unit 400manually, for instance by laterally shifting the handlebar 20.

The configuration that is schematically depicted in FIG. 19 cantransport a generator 80 having a relatively large power capacity insidethe drive unit 400. The generator 80, as well as all other components,are then well protected and sheltered inside the housing.

FIG. 20 illustrates a single housing 450 that is similar to that of FIG.19 but where the motors are electric motors 310 powered by the batteries312. It is also possible to provide only one electric motor 310 in someembodiments. This configuration will create an electric dumper when thedrive unit 400 is provided with a dump body 410 as in FIGS. 11 and 12.The housing 450 with the largest volume that is schematically depictedin FIG. 20 allows using larger batteries 312, thus more powerfulbatteries compared to those of the juxtaposed apparatuses 10. In allcases, it would be possible to provide an electrical power converter,for instance DC to AC, to supply power for a domestic power outlet orothers.

FIG. 21 is a schematic view of an embodiment in which are providedaltogether an internal-combustion engine 32, a generator 80, twoelectric motors 310 and two sets of batteries 312. This is thus a modelof drive unit 400 said to be “hybrid”. In this case, the operator and/ora control system can determine which among the two modes (mechanical orelectrical) must be used. It could also be possible to use bothsimultaneously.

Many other configurations are possible. For instance, it could bepossible to have an internal-combustion engine 32 that is only connectedto a generator 80, which internal-combustion engine 32 does not directlydrive the tracks 12 through a mechanical connection. Power to drive thetracks 12 is then supplied through the electric motors 310.

FIG. 22 is a block diagram that schematically shows an example of acontrol arrangement for the drive unit 400. In this example,potentiometers 500 are provided on the handles of the handlebar 20. Eachpotentiometer 500 measures the position of a corresponding command leverand sends electric signals or something else to the control unit 502,for instance an onboard computer or a dedicated electronic circuit.These signals are computed by the control unit 502 in order to establishthe rotation speed of each track 12. The command signals are sent inthis example to electric motors 310, each motor 310 corresponding to oneof the tracks 12. Many other variants are possible. This also includeshaving mechanical-type commands between the handles and the commandunit. The levers on the handles could then move metallic rods so as tomechanically transmit the position of each lever to another location onthe drive unit 400.

FIG. 23 is a top view of an example of a drive unit 400 according to theproposed concept. This version is substantially similar to that shown inFIG. 16. It includes two juxtaposed apparatuses 10. Each apparatus 10includes an electric motor 310 and a corresponding set of batteries 312.

FIG. 24 is a view similar to FIG. 23 and illustrates another example ofa drive unit 400 according to the proposed concept. This version issubstantially similar to that schematically depicted in FIG. 19. Itincludes an internal-combustion engine 32, a generator 80 and atransmission 60. The various components are disposed to balance theweight in an optimized fashion. For instance, the internal-combustionengine 32 and the generator 80 are positioned along the central axis ofthe drive unit 400.

The proposed concept thus allows manufacturing drive units 400 that arevery compact, highly performant and that provide an optimum groundbearing while keeping dimensions small in order to reach places veryrestricted in terms of space. Unlike previously-proposed apparatuses,the tracks 12 can easily cover almost the entire surface that isdirectly underneath the drive unit 400 and can bring the height of thecenter of gravity to a minimum never seen before. Very heavy payloadscan thus be easily transported to places where it was almost impossibleto go before.

The present detailed description and appended figures are only examples.A person working in this field will be able to see that variants can bemade while still staying within the framework of the proposed concept.

What is claimed is:
 1. A transport drive unit, including: two compactpulling apparatuses that are juxtaposed and rigidly paired, eachapparatus including: a watertight elongated housing extending along alongitudinal axis and defining an inner chamber, the housing including atop wall and a bottom wall; a track disposed around the housing alongits longitudinal axis; a track-driving motor, the motor being locatedwithin the inner chamber of the housing and including an output shaftmechanically connected to the track; and a ventilation circuit for theinner chamber of the housing, the ventilation circuit including an airinlet and an air outlet which communicate with outside of the housing,the ventilation circuit allowing the temperature within the innerchamber to be kept above the freezing point when the outside temperatureis lower and allowing the interior of the inner chamber to be cooledwhen its temperature exceeds an upper threshold.
 2. The drive unitaccording to claim 1, wherein the motor of at least one of theapparatuses is an internal-combustion engine supplied with fuel from atank located inside the corresponding inner chamber.
 3. The drive unitaccording to claim 2, wherein at least one of the apparatuses includes agenerator located inside the corresponding inner chamber.
 4. The driveunit according to claim 2, wherein in each apparatus, the air inlet ofthe corresponding ventilation circuit includes an air inlet box locatedabove the corresponding inner chamber.
 5. The drive unit according toclaim 4, wherein the air inlet box of each apparatus includes apertureslocated on at least one exterior side, each aperture being incommunication with an air outlet of the corresponding air inlet box. 6.The drive unit according to claim 2, wherein the engine includes anexhaust pipe, the exhaust pipe having a first end connected to theengine and a second end exiting outside of the corresponding innerchamber.
 7. The drive unit according to claim 1, wherein the motor of atleast one of the apparatuses is an electric motor powered by at leastone battery located inside the corresponding inner chamber.
 8. The driveunit according to claim 1, wherein the ventilation circuit of the innerchamber of at least one of the apparatuses includes a thermostat.
 9. Thedrive unit according to claim 1, wherein the two apparatuses are pairedthrough adjacent lateral walls of the apparatuses.
 10. The drive unitaccording to claim 1, wherein the inner chamber of the two apparatusesis maintained at a positive pressure with reference to the atmosphericpressure.
 11. The drive unit according to claim 1, further including ahandlebar connected to the housings of the apparatuses and that extendssubstantially rearwards.
 12. The drive unit according to claim 1,wherein the drive unit includes a transport rack located above thetracks and that is connected to the housings.
 13. The drive unitaccording to claim 12, wherein the transport rack includes a dump body.14. The drive unit according to claim 13, wherein the dump body ismechanically tilted using a motorized arrangement provided on the driveunit.
 15. The drive unit according to claim 14, wherein the drive unitincludes a rear platform to transport an operator.
 16. A transport driveunit, including: a watertight elongated housing extending along alongitudinal axis and defining an inner chamber, the housing including atop wall and a bottom wall; two juxtaposed tracks, disposed in parallelaround the housing along the longitudinal axis, allowing the drive unitto move when the tracks are driven in rotation around the housing; atleast one track-driving motor, the motor being located in the innerchamber of the housing and including an output shaft that ismechanically connected to at least one of the tracks; a ventilationcircuit for the inner chamber of the housing, the ventilation circuitincluding an air inlet and an air outlet which communicate with outsideof the housing, the ventilation circuit allowing the interior of theinner chamber to be kept above the freezing point when the outsidetemperature is lower and allowing the inner chamber of the housing to becooled when the outside temperature is above an upper threshold; atransport rack located above the tracks and that is connected to thehousing; and a dump body provided on the transport rack.
 17. The driveunit according to claim 16, further including at least one generatorlocated within the inner chamber.
 18. The drive unit according to claim16, wherein the inner chamber is maintained at a positive pressure withreference to the atmospheric pressure.
 19. The drive unit according toclaim 16, wherein the dump body is mechanically tilted using a motorizedarrangement provided on the drive unit.
 20. The drive unit according toclaim 16, wherein the drive unit includes a rear platform to transportan operator.